Portable data transmitting/receiving apparatus, such as a TDD (Telecommunications Device for the Deaf), is not always used in a location that permits convenient connection to the Public Switched Telecommunications Network (PSTN). Moreover, such apparatus can be made less expensive and more portable by eliminating dialing circuitry and other electrical equipment needed for interconnection with the PSTN. The idea of acoustically coupling signals between the apparatus and a conventional telephone handset has been around for many years to satisfy this need. However, one of the problems associated with acoustic coupling has been the inability to operate with a variety of different handset shapes and in various environments--including those where the ambient noise level is high.
Coupling efficiency between the handset and a handset-coupling device (cradle) on the apparatus has been improved by the use of compliant seals in the cradle that conform to the shape of the handset. Perhaps the most well-known seals used in such devices are rubber cups that are shaped to individually enclose the handset's mouthpiece and earpiece. Rubber cups are particularly well suited to seal certain handset shapes such as AT&T's model "G" handset which has circularly shaped mouthpiece and earpiece regions. The rubber cups not only reduce ambient noise, but they also provide a sealed enclosure similar to the one created when the receiver is held tightly against the user's ear. This sealed enclosure provides the proper acoustic impedance match for conventional receivers which is needed for signal coupling efficiency--otherwise acoustic signals are degraded.
Over the years, telephone handset shapes have proliferated to such a degree that many no longer fit into the rubber cups that cooperate so well with "G" handsets. Additionally, users have complained that the rubber cups form such good seals with "G" handsets that they are quite difficult to insert and remove.
Accordingly, it is desirable to provide a cradle for coupling signals between a telephone handset and a data terminal, or similar equipment, that improves existing acoustic coupling techniques. It is also desirable that the cradle be suitable for a variety of handset sizes and shapes. Finally, it is desirable that the cradle allow easy insertion and removal of the telephone handset.